This invention relates to liquid treating units.
Liquid treating units are known which incorporate a semipermeable membrane for removing dissolved inorganic or organic substances from aqueous solutions or for the separation or concentration of high-molecular-weight substances such as proteins, starches and colloidal dispersed materials. Such known liquid treating units are divided into five general types according to the shape of the semipermeable membrane used: the tubular type (U.S. Pat. No. 3,616,929, No. 3,769,128 and No. 3,873,665), the hollow fiber type (U.S. Pat. No. 3,442,002, No. 3,339,341 and No. 3,246,764), the plate-and-frame type (Japanese Patent Application Disclosure No. 70280/1975), the spiral type (U.S. Pat. No. 3,542,203, No. 3,554,378 and No. 3,746,591) and the pleat type (Japanese Patent Application Disclosure No. 802791975). Of these, the spiral type which is simple in construction is most widely used, whereas the pleat type has not been in wide use.